Material handling vehicles with boom arms and buckets are used in the construction and agricultural industries to move material such as earth. An operator will use the boom arm to raise the bucket off the ground so that the material can be placed in a dump truck or other location. Often the desired location is at a substantial height above ground and a considerable distance in front of the loader.
Conventional loaders for tractors typically comprise a two-piece boom arm having a lower arm pivotally connected to the frame of the tractor and an upper arm rigidly connected to the lower arm at a fixed angle that provides clearance for the front wheels of the tractor. However, the use of a fixed angle boom arm limits the maximum height elevation and forward extension of the boom arm. This limitation restricts where an operator can place material using the bucket, making some remote locations inaccessible to the operator.
Conventional loaders can be sized to provide extra height and forward extension. However, the boom arms for these loaders tend to be significantly larger, more cumbersome, and more expensive than the boom arms for traditional small loaders for tractors.
Other prior art loaders, such as large excavators, have a two-piece boom arm comprising a lower arm pivotally attached to the vehicle, and an upper arm pivotally attached to the lower arm. The lower arm is raised and lowered by extension and retraction of a hydraulic cylinder connected between the vehicle and lower arm. The upper arm is rotated by the extension and retraction of a second hydraulic cylinder connected between the lower arm and the upper arm. A third hydraulic cylinder, connected between the upper arm and bucket, controls the tilt of the bucket. When the boom arm is in the lowered position, the operator can set the angle between the lower and upper arm to ensure that wheel clearance is maintained. In the raised position, the operator can rotate the upper arm so that it is parallel with the lower arm, providing additional bucket elevation and forward reach.
The major drawback of this type of loader boom arm is that the lower and upper arms must be controlled independently using two different controls. Simultaneous movement of both arms is further complicated by having the upper arm rotating relative to the motion of the lower arm. In addition to the dual boom arm operation, the operator must also control the tilt of the bucket, which moves in relation to the both the lower arm and the upper arm. The added complication of operating all three device independently means that more experienced and highly trained workers are required to operate large excavators. Even then, very few operators can master the precise art of moving the three devices simultaneously.
Another problem with conventional loaders is the design of self leveling linkage assemblies that maintain a level bucket during raising and lowering of a boom arm. Conventional self leveling linkages have a rod that is offset above the main boom arm. Due to its high profile, the rod may obstruct an operator's view, preventing accurate use of the boom arm and bucket. Furthermore, since the rod extends along the entire length of the boom arm, it requires a substantial amount of material, which is undesirable from a manufacturing and cost perspective.
Accordingly, there is a need for a loader boom arm that can provide additional elevation and/or forward extension of a bucket without increasing the difficulty level associated with operating the boom arm. There is also a need for a loader boom arm having a self leveling linkage that does not obstruct the view of an operator.